The present invention relates to an apparatus for supplying breathable gas.
The present invention has been developed primarily for use in Continuous Positive Airway Pressure (CPAP) treatment of, for example, Obstructive Sleep Apnea (OSA) in which pressurised air is supplied to a patient""s airways to pneumatically splint them open. The pressure of the gas supplied to the patient can be constant, bi-level (in synchronism with patient breathing) or auto-setting in level. Throughout this specification any reference to CPAP is intended to incorporate a reference to any one of, or combinations of, these forms of pressurised gas supply.
The invention is also suitable for supplying gas for assisted respiration or mechanical ventilation.
Some people find breathing the cool, dry air produced by the flow generator of a gas supplying apparatus uncomfortable, leading to possible lack of treatment compliance. It can also cause a dry or runny nose. This problem can be ameliorated by placing a humidifier in the gas flow path between the flow generator and the patient to moisturize the gas supplied to the patient. A humidifier basically is a reservoir of water over the surface of which the pressurised breathable gas flows. The water can be heated (known as an xe2x80x9cactivexe2x80x9d humidifier) or unheated (known as xe2x80x9cpassivexe2x80x9d).
In some gas supply apparatus, in particular those used in CPAP treatment, it is desirable or necessary to monitor the pressure of the gas being supplied at the mask worn on the patient""s face. This is generally done by monitoring the pressure at the flow generator with an electronic pressure transducer and then compensating for the known flow characteristics of the delivery tube and mask by calibration to determine the mask treatment pressure.
However, if a humidifier is placed between the flow generator and the mask (downstream of the pressure transducer) its pneumatic impedance of the gas flow may result in large pressure swings and the introduction of errors into the mask pressure calculation. Moreover, if the pressure signal is used to measure snore as an indication of partial apnea, the humidifier may muffle the snore component thereby reducing the accuracy of the snore measurement.
It is known to ameliorate these problems by using a hollow cylindrical plug having a pressure sensing port connected by a flexible tube to a pressure transducer mounted within the housing that contains the flow generator. If the apparatus is used without a humidifier the plug has one end connect directly to the flow generator outlet and the other connected to the mask supply tube inlet. When a humidifier is used, the humidifier inlet is connected to the flow generator outlet and the humidifier outlet is connected to one end of the plug. The other end of the plug remains connected to the mask supply tube inlet. In this way, the pressure monitored by the pressure transducer is downstream of the humidifier and not affected by its alteration of the gas supply path.
However, this apparatus suffers from several problems. Firstly, the usage of the plug and associated tube is messy and unsightly. Further, the tube is thin and prone to kinking and/or squashing leading to inaccuracies in pressure measurement, Also, if the tube is removed and inadvertently replaced with a tube of different length or diameter, the accuracy of the mask pressure calculation is adversely affected. Finally, the apparatus suffers from the possibility that the humidifier or plug may be incorrectly installed, particularly when used by patients in the home and/or with humidifiers manufactured by a third party.
The above disadvantages may be ameliorated by incorporating a humidifier into the housing that contains the flow generator. However, this is uneconomical as many patients do not require this feature.
Accordingly, there exists a need for an apparats for supplying breathable gas which can be easily and simply connected to a humidifier and which may also be quickly and simply configured to function without a humidifier, in which gas supply pressure is sensed downstream of the humidifier, if present.
The present invention is directed towards achieving one or more of these needs and, in particular, to substantially overcoming or at least ameliorating one or more of the disadvantages of the existing apparatus described above.
Accordingly, in the first aspect, the present invention discloses an apparatus for supplying breathable gas, the apparatus includes:
a flow generator;
a gas outlet;
a connection mans interposed between the flow generator and the gas outlet, the connection means having a connection inlet and a connection outlet; and
a pressure sensing means interposed between the connection outlet and the gas outlet, wherein the connection means is adapted to allow selective connection to either a duct member providing a direct flow path from the connection inlet to the connection outlet or to a humidifier interposed between the connection inlet and the connection outlet.
The connection inlet receives gas from the flow generator. The connection outlet receives gas from the humidifier or the duct member, as the case may be.
Preferably, the breathable gas is air,
Desirably, the apparatus is connected by a gas supply tube to a patient xe2x80x9cmaskxe2x80x9d to provide CPAP treatment, assisted respiration or mechanical ventilation. Mask varieties include nose masks, mouth masks, combination nose and mouth masks, nasal prongs, nasal pillows and fill face masks.
The pressure sensing means is preferably an electronic pressure transducer.
The connection inlet and the connection outlet may be identical or may be different, for example in cross-sectional shape or diameter, in order to avoid incorrect installation of the duct member or the humidifier.
Preferably, the connection inlet and the connection outlet are recessed behind the outer edge of the casing or housing of the apparatus. In an embodiment, the duct member is in the form of a substantially U-shaped pipe adapted to connect the connection inlet and the connection outlet, The pipe preferably has an outer panel attached thereto which, upon installation, is substantially flush with adjacent outer panels of the casing or housing. In a preferred form the U-shaped pipe is comprised of two joined sections encased in a shape having a snap-engageable base and lid.
The humidifier can include a heater (ie. active) or be unheated (ie. passive).
In an embodiment, the apparatus also includes a gas flow rate sensing means interposed between the connection outlet and the gas outlet. In one form, the gas flow rate sensing means is a pressure differential flow sensor communicating with two pressure ports, the ports being respectively disposed on opposite sides of a flow impedance. In a preferred form, one of the pressure ports, preferably the port closest to the gas outlet, also communicates with the pressure sensing means.
The duct-member, and other components in the gas path, are desirably produced from antimicrobial materials. The duct member, and other components in the gas path, are also desirably disposable.
In a second aspect, the present invention discloses a CPAP treatment device incorporating the apparatus of the first aspect.